Resin and the Resistance of Conifers to Fomes annosus

Roots of young trees of different conifer species, Scots pine,Corsican pine, Sitka spruce, and Douglas fir were inoculatedwith Fomes annosus. In the pines, infection was negligible butin the other genera the central wood was extensively invaded.The process of infection was studied further in Sitka spruceby means of a root-severing technique in which an inoculum blockwas forced between the cut ends of a root. In most trees a centralrot developed which in some extended up into the butt: the meanextent of growth recorded was 30 cm in 14 months. In the severedroot portions infection also occurred but F. annosus was subsequentlyreplaced to a considerable extent by other micro-organisms,particularly in trees growing on a peat soil. A similar centralrot developed after inoculations of Norway spruce. The resistance of pine sapwood and the outer wood of spruceand Douglas fir can be explained at least partially by the structureand viability of the resin duct system. Larch, Douglas fir,spruce, and pine form a series showing increasing complexityand activity of the resin system. In addition, studies carriedout on the resin yields of pines growing under different conditionsshowed that the resistance of a tree to F. annosus is correlatedwith its ability to mobilize resin. Site factors, forest management,host age vigour, genetic constitution, and past history mayall influence resin mobilization.